Many hardwired communications systems use plug and jack connectors to connect a communications cable to another communications cable or to a piece of equipment such as a computer, printer, server, switch or patch panel. By way of example, high speed Ethernet communications systems routinely use such plug and jack connectors to connect computers, printers and other devices to local area networks and/or to external networks such as the Internet. FIG. 1 depicts a highly simplified example of such a hardwired high speed communications system that illustrates how plug and jack connectors may be used to interconnect a computer 11 to, for example, a network server 20.
As shown in FIG. 1, the computer 11 is connected by a cable 12 to a communications jack 15 that is mounted in a wall plate 19. The cable 12 is a patch cord that includes a communications plug 13, 14 at each end thereof. Typically, the cable 12 includes eight insulated conductors, and the communications plug 14 and the communications jack 15 will typically each have eight contacts. As shown in FIG. 1, plug 14 is inserted into an opening or “plug aperture” 16 in the front side of the communications jack 15 so that the contacts or “plug blades” of communications plug 14 mate with respective contacts of the communications jack 15. The communications jack 15 includes a wire connection assembly 17 at the back end thereof that receives eight conductors from a second cable 18 that are individually pressed into slots in the wire connection assembly 17 to establish mechanical and electrical connections between each conductor of the second cable 18 and a respective one of a plurality of conductive paths through the communications jack 15. The other end of the second cable 18 is connected to a network server 20 which may be located, for example, in a telecommunications closet of a commercial office building. Communications plug 13 similarly is inserted into the plug aperture of a second communications jack (not pictured in FIG. 1) that is provided in the back of the computer 11. Thus, the patch cord 12, the cable 18 and the communications jack 15 provide a plurality of electrical paths between the computer 11 and the network server 20. These electrical paths may be used to communicate electrical information signals between the computer 11 and the network server 20. Most modern conductive-wire based communications systems of the type depicted in FIG. 1 use industry standardized plugs and jacks that conform the “RJ-45” plug and jack specifications.
When an information signal is transmitted over a conductor such as an insulated copper wire in a communications cable, electrical noise from external sources may be picked up by the conductor, degrading the quality of the information signal. In order to counteract such noise sources, the information signals in the above-described communications systems are typically transmitted between devices over a pair of conductors (hereinafter a “differential pair” or simply a “pair”) rather than over a single conductor. The two conductors of each differential pair are twisted tightly together in the communications cables and patch cords so that the eight conductors are arranged as four twisted differential pairs of conductors that form four differential transmission lines. The signals transmitted on each conductor of a differential pair have equal magnitudes, but opposite phases, and the information signal is embedded as the voltage difference between the signals carried on the two conductors of the pair. When the information signal is transmitted over a twisted differential pair of conductors, each conductor in the differential pair often picks up approximately the same amount of noise from these external sources. Because approximately an equal amount of noise is added to the signals carried by both conductors of the twisted differential pair, the information signal is typically not disturbed, as the information signal is extracted by taking the difference of the signals carried on the two conductors of the differential pair, and this subtraction process may mostly cancel out the noise signal.
Unfortunately, the proximities of the conductors and contacting structures within each plug-jack connection (e.g., where plug 14 mates with jack 15) can produce capacitive and/or inductive couplings. These capacitive and inductive couplings in the connectors (and similar couplings that may arise in the cabling) give rise to another type of noise that is known as “crosstalk.” “Crosstalk” is typically defined as the unwanted signal energy that is capacitively and/or inductively coupled onto the conductors of a first “victim” differential pair from a signal that is transmitted over a second “disturbing” differential pair.
While methods are available that can significantly reduce the effects of crosstalk within communications cable segments, the communications connector configurations that were adopted years ago—and which still are in effect in order to maintain backwards compatibility—generally did not maintain the arrangement and geometry of the conductors of each differential pair so as to minimize the crosstalk coupling between the differential pairs in the connector hardware. For example, pursuant to the ANSI/TIA-568-C.2 standard approved Aug. 11, 2009 by the Telecommunications Industry Association (also known as the Category 6a standard), the eight plug blades, and hence the plug blade contact regions of the eight jack contacts 1-8, must be aligned in a row. FIG. 2 shows the positions and pair assignments of the plug contact regions of the eight jack contacts 1-8. As is apparent from FIG. 2, this arrangement of the eight jack contacts 1-8 will result in unequal coupling between the differential pairs, and hence crosstalk is introduced.
As the operating frequencies of communications systems has increased, crosstalk in the plug and jack connectors has became a more significant problem. The crosstalk that is introduced in an RJ-45 plug and the additional crosstalk that is generated in the mating region of an RJ-45 jack is typically referred to as “offending crosstalk.” While offending crosstalk is generated between all four differential pairs in an RJ-45 plug, the crosstalk is particularly problematic between pairs 1 and 3 due to the “split pair” arrangement, and is also significant between pair 2 and pair 3 and between pair 3 and pair 4.
To address the crosstalk problem, communications jacks were developed that included so-called “compensating crosstalk circuits” that introduce compensating crosstalk that was used to cancel much of the offending crosstalk that is introduced in the plug-jack mating region as a result of the industry-standardized connector configurations. In order to ensure that plugs and jacks manufactured by different vendors would operate properly, industry standards were developed that, among other things, tightly specified the amount of offending crosstalk that would exist between each of the differential pairs in an RJ-45 plug. By standardizing this parameter, manufacturers could design their RJ-45 jacks to cancel the amounts of crosstalk specified in the industry standards using various crosstalk compensation circuits that are known to those of skill in the art.